When combusting fossil fuels in power generating plants, the question of CO2 emission acquires increasing significance in the course of climate discussion.
So-called “polygeneration” systems or plants, in which a synthesis gas, gaseous nitrogen and liquid hydrogen are produced from a carbonaceous feedstock, such as coal, by gasification and reforming, are known (see, for example, U.S. Pat. No. 4,936,869). The synthesis gas is fed for combusting to the combustion chamber of a gas turbine installation, which is part of a combined cycle power plant, and with the hot exhaust gases from the gas turbine steam is produced in a water/steam cycle for operating a steam turbine. The two turbines generate electric power, while some of the steam which is produced is used for reforming. In addition, thermal energy for process or heating purposes can be extracted from the combined cycle power plant. The electric power which is generated can be used in the plant itself, but can also be delivered to external consumers. The hydrogen which is produced, which can be of high purity (99.9%), can be used for example for chemical processes such as the production of artificial fertilizers.
If in the case of such a plant the fuel for the gas turbine should contain a high portion of hydrogen, if the CO2 which results during the gasification were to be separated out, the emission of CO2 with the exhaust gases of the gas turbine would be low (would correspond to an approximately 90% retention of CO2). Such “CO2-free” power generating plants, however, would be ready for operation only when fuels with a high hydrogen portion could be combusted in a gas turbine (with or without sequential combustion) reliably and without significant dilution. In order to achieve an approximately 90% retention of CO2, however, an effective development of new burner technologies would be necessary, which are currently not available.
Furthermore, gas turbine installations with sequential combustion have been known for a long time (see, for example, D. K. Mukherjee, “State-of-the-art gas turbines—a brief update”, ABB Review February 1997, p. 4-14 or F. Joos et al., “Field experience with the sequential combustion system of the GT24/GT26 gas turbine family”, ABB Review May 1998, p. 12-20). For such gas turbine installations, proposals for reducing CO2 emission, which are based on exhaust gas recycling (see, for example, US-A1-2006/0272331), have already been made. Such gas turbine installations with sequential combustion, however, have already been used as part of a combined cycle power plant with integrated coal gasification (see, for example, WO-A1-2007/017486), wherein the syngas which is produced during gasification is used as fuel both in the first combustion chamber and in the second combustion chamber.
In the case of the known gas turbine installations with sequential combustion (see EP-0 620 362 A1), so-called EV burners are used in the first combustion chamber (see EP 0 321 809 A1 and the developments carried out since then). In the second combustion chamber, so-called SEV burners are correspondingly incorporated (see the abovementioned printed publications). In the past, particularly high-capacity burner types have been developed for the first combustion chamber (so-called AEV burners or Advanced EV burners) (B. Nilsson, “GTX100—a new high-performance gas turbine” ABB Review June 1997, p. 4-12, FIG. 3; WO-A1-2006/069861, or EP-0 704 657 A2 and further developments derived therefrom), which are formed as premix burners in which gaseous fuels are injected both in a premix device and in a subsequent mixer tube.
Finally, a gas turbine installation with CO2 separation, which comprises two separate gas turbine systems which in each case have a compressor, a combustion chamber and a turbine, is known from EP-A2-1 741 899. Some of the air which is compressed in the first compressor in this case is fed to the second combustion chamber as combustion air, while the exhaust gases of the second turbine are fed back to the second compressor and also compressed there. CO2 is then separated out from the compressed gases. Both gas turbine systems are linked in each case to a combined cycle power plant via a heat recovery steam generator with a water/steam cycle. In the first combustion chamber, pure hydrogen is combusted, and in the second combustion chamber for example natural gas can be used as fuel. The hydrogen can be supplied externally or can be produced by internal reforming. As a result of operating the one (first) combustion chamber with pure hydrogen, if the CO2 which results during hydrogen production is separated out, the CO2 emission is already significantly reduced. In this case, however, it is disadvantageous that the first gas turbine system has to be designed for operating with pure hydrogen, which is not the case in already existing or fully developed plants.
All the printed publications which are quoted above form an integrating element of this description.